Focal plane wavefront sensor achromatization : The multireference self-coherent camera

Abstract

High contrast imaging and spectroscopy provide unique constraints for exoplanet formation models as well as for planetary atmosphere models. But this can be challenging because of the planet-to-star small angular separation and high flux ratio. Recently, optimized instruments like SPHERE and GPI were installed on 8m-class telescopes. These will probe young gazeous exoplanets at large separations (~1au) but, because of uncalibrated aberrations that induce speckles in the coronagraphic images, they are not able to detect older and fainter planets. There are always aberrations that are slowly evolving in time. They create quasi-static speckles that cannot be calibrated a posteriori with sufficient accuracy. An active correction of these speckles is thus needed to reach very high contrast levels (>1e7). This requires a focal plane wavefront sensor. Our team proposed the SCC, the performance of which was demonstrated in the laboratory. As for all focal plane wavefront sensors, these are sensitive to chromatism and we propose an upgrade that mitigates the chromatism effects. First, we recall the principle of the SCC and we explain its limitations in polychromatic light. Then, we present and numerically study two upgrades to mitigate chromatism effects: the optical path difference method and the multireference self-coherent camera. Finally, we present laboratory tests of the latter solution. We demonstrate in the laboratory that the MRSCC camera can be used as a focal plane wavefront sensor in polychromatic light using an 80 nm bandwidth at 640 nm. We reach a performance that is close to the chromatic limitations of our bench: contrast of 4.5e-8 between 5 and 17 lambda/D. The performance of the MRSCC is promising for future high-contrast imaging instruments that aim to actively minimize the speckle intensity so as to detect and spectrally characterize faint old or light gaseous planets.

14 pages, 20 figures

References in corpus (5)

• Direct Imaging of Multiple Planets Orbiting the Star HR 8799
• Wide-Field InfrarRed Survey Telescope-Astrophysics Focused Telescope Assets WFIRST-AFTA 2015 Report
• Wavefront error correction and Earth-like planet detection by Self-Coherent Camera in space
• From Cosmic Birth to Living Earths: The Future of UVOIR Space Astronomy
• An Eight-Octant Phase-Mask Coronagraph

Cited by in corpus (13)

• SPHERE: the exoplanet imager for the Very Large Telescope
• The self-coherent camera as a focal plane fine phasing sensor
• Comparing focal plane wavefront control techniques:\\Numerical simulations and laboratory experiments
• Imaging exoplanets with coronagraphic instruments
• Laboratory validation of the dual-zone phase mask coronagraph in broadband light at the high-contrast imaging THD-testbed
• Minimization of non common path aberrations at the Palomar telescope using a self-coherent camera
• Status and performance of the THD2 bench in multi-deformable mirror configuration
• The spectrally modulated self-coherent camera (SM-SCC): Increasing throughput for focal-plane wavefront sensing
• Review of high-contrast imaging systems for current and future ground-based and space-based telescopes II. Common path wavefront sensing/control and Coherent Differential Imaging
• The polarization-encoded self-coherent camera
• Fast focal plane wavefront sensing on ground-based telescopes
• Comparative laboratory study of electric field conjugation algorithms
• First Experimental Results of the Fast Atmospheric Self-coherent Camera Technique on the Santa cruz Extreme Adaptive optics Laboratory Testbed: Demonstration of High Speed Focal Plane Wavefront Control of Residual Atmospheric Speckles